1. Field of the Invention
The present invention relates to a semiconductor device and a semiconductor device manufacturing method.
2. Related Art
In a case that a polysilicon gate electrode is used, the gate electrode is liable to be depleted when a voltage is applied to the gate electrode. The depleted gate electrode is disadvantageous in that an inverting capacity of a channel region is reduced. A metal gate electrode is employed to suppress the depletion of the gate electrode. A full silicide gate electrode is developed as a kind of the metal gate electrode. The full silicide gate electrode is a gate electrode silicided by reacting an overall polysilicon gate with a metal such as nickel and the like.
Further, recently, as a gate dielectric film is increasingly reduced in thickness and the dielectric constant thereof is more increased, it is contemplated to use a high dielectric material such as HfSiON, HfO2, and the like as the gate insulation film. When the high dielectric material is used as the gate insulation film, a threshold voltage of a p-type MISFET (Metal-Insulator Semiconductor Field-Effect Transistor) greatly shifts to a negative side. The change of the threshold voltage is observed even if the full silicide gate electrode is employed.
Heretofore, a large amount of an impurity is implanted in a gate electrode to suppress change of the threshold voltage of the p-type MISFET and to employ the full silicide gate electrode (Kedzierski et al. IEDM Tech. Dig. 247(2002) and Kedzierski et al IEDM Tech. Dig. 315(2003)). However, when a large amount of dopant is implanted, a p-type impurity (in particular, boron) penetrates to a semiconductor substrate, from which a problem arises in that the threshold voltage disperses and a carrier mobility is deteriorated.
In contrast, when a metal rich silicide, which contains a metal in an amount larger than that of an n-type MISFET, is used as a gate electrode of a p-type MISFET, the threshold voltage of the p-type MISFET is set to a proper value even if a gate insulation film is composed of a high dielectric material (Takahashi et al. IEDM Tech. Dig. 91(2004)). However, when the same metal rich silicide is applied to a gate electrode of an n-type MISFET, a problem arises in that a threshold voltage of the n-type MISFET shifts from a proper value.